The present disclosure herein relates to an electronic device, and more particularly, to a semiconductor memory device and a data processing method thereof.
Generally, a semiconductor memory is a micro electronic device that is most essential for the designs of digital logics such as applications and computers based on a microprocessor belonging to a range from a satellite to a consumer electronic technology. Therefore, the advance of the fabrication technology of a semiconductor memory including the improvement of processes and the development of technologies, obtained though scaling for high speed and a high degree of integration, is helped to establish another digital logic-based performance reference.
A semiconductor memory device is largely divided into a volatile semiconductor memory device and a nonvolatile semiconductor memory device. The nonvolatile semiconductor memory device may store data even when a power source is shut off. Data stored in a nonvolatile memory may be permanent or be reprogrammed according to a memory fabrication technology. The nonvolatile semiconductor memory device is used to store programs and micro codes in wide applications such as computers, avionics, communications and consumer electronic technology industry.
A flash memory device is included in a representative example of the nonvolatile memory device. Recently, as high integration requirements for memory devices increase, multi-bit memory devices that store multi bits in one memory cell are generalized. In the memory cells of the multi-bit flash memory device, intervals between threshold voltage distributions should be densely controlled. That is, data retention characteristic is most important in association with the reliability of data. However, the threshold voltages of memory cells may be changed due to various factors. Electric charges (or electrons) stored in floating gates may be leaked through various failure mechanisms such as thermion emission, electronic charge spreading, ion impurities and programming disturbance stress due to the defect of a dielectric layer. This may cause the shift of threshold voltages. In a state where the control gates of memory cells are kept at a certain voltage (for example, a power source voltage or a read voltage), when the floating gates gradually obtain electric charges, electric charges can be obtained due to read disturbance. This causes the increase of the threshold voltages. Due to the various factors, the threshold voltages of memory cells may increase or decrease for each state. In a Charge Trapping Flash (CTF) memory device, particularly, issues such as lateral charge spreading become important. In a multi-bit memory device for storing a more number of data in one memory cell, technologies for solving these limitations are necessarily required.